<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=1200, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>click</button>

    <script>
        const oButton = document.querySelector('button')
        const callback = function () {
            console.log('Hello, Event')
        }

        oButton.addEventListener('click', callback)
        oButton.addEventListener('click', ()=> {
            console.log('hello, event1')
        })

    </script>
</body>
</html>